The melt flow rate (MFR) of a polymer resin is a function of its molecular weight. In general, increasing the melt flow rate allows the resin to be processed at lower temperatures and to fill complex part geometries. Various prior art methods of increasing the melt flow rate involve melt-blending the resin in an extruder with a compound capable of generating free radicals, such as a peroxide. The weight average molecular weight of the polymer is reduced and the MFR is increased. Increasing the melt flow rate by decreasing the molecular weight of the polyolefin polymer, however, has been found in many cases to have a detrimental effect on the strength of the modified polymer. For example, decreasing the molecular weight of the polymer can significantly lower the impact resistance of the polymer. And this lowered impact resistance can make the polymer unsuitable for use in certain applications or end uses. Accordingly, when extant technologies are utilized, one must strike a compromise between increasing the melt flow rate and undesirably decreasing the impact resistance of the polymer. This compromise often means that the melt flow rate is not increased to the desired level, which requires higher processing temperatures and/or results in lower throughputs.
A need therefore remains for additives and processes that can produce polymer compositions having an increased melt flow while preserving, or even improving, the impact resistance of the polymer.